Most commercially available cardiac pacing and defibrillation leads are placed by means of a stylet which is inserted into a central lumen through the lead, and is used to assist in pushing the lead through the vascular system and guiding it to a desired location. A guidewire, possessing a smaller diameter than a stylet, may also be used to place a lead. Guidewires extend entirely through the lead and out its distal end. The approach of using a guidewire to place cardiac pacing leads and cardioversion leads is disclosed in U.S. Pat. No. 5,003,990 issued to Osypka, U.S. Pat. No. 5,755,765 issued to Hyde et al, U.S. Pat. No. 5,381,790 issued to Kenasaka and U.S. Pat. No. 5,304,218 issued to Alferness.
Lead placement into the left heart is difficult since the veins are very small. Consequently, a stylet is initially used to get the lead down to the right atrium and locate the left coronary vein returning from the left outer area of the heart. From that point, a stylet is considered too big to enter the small left ventricle veins. The guidewire is then used for final placement of the lead in the small left ventricle veins.